Carbon-based material and method of producing the same, and composite material and method of producing the same

ABSTRACT

A method of producing a carbon-based material includes steps (a), (b) and (c). In the step (a), an elastomer and at least a first carbon material is mixed and the first carbon material is dispersed by applying a shear force to obtain a composite elastomer. In the step (b), the composite elastomer is heat-treated to vaporize the elastomer, and a second carbon material is obtained. In the step (c) the second carbon material is heat-treated together with a substance including an element Y to vaporize the substance including the element Y, a melting point of the element Y being low.

This is a Continuation of application Ser. No. 11/214,737 filed Aug. 31,2005. The entire disclosure of the prior application is herebyincorporated by reference in its entirety. Japanese Patent ApplicationNo. 2004-257440, filed on Sep. 3, 2004, is hereby incorporated byreference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a carbon-based material and a method ofproducing the same, and a composite material and a method of producingthe same.

A composite material using a carbon material such as carbon fiber,carbon black, graphite, or carbon nanofiber has attracted attention (seeJP-A-5-78110, for example). Such a composite material is expected toexhibit improved electric conductivity, heat transfer properties, andmechanical strength due to inclusion of the carbon material such ascarbon nanofiber.

However, the carbon material generally exhibits low wettability(affinity) with a matrix material of the composite material and exhibitslow dispersibility in the matrix material. In particular, since thecarbon nanofibers have strong aggregating properties, it is verydifficult to uniformly disperse the carbon nanofibers in a matrix of thecomposite material. Therefore, it is difficult to obtain a carbonnanofiber composite material having desired properties. Moreover,expensive carbon nanofibers cannot be efficiently utilized.

SUMMARY

A first aspect of the invention relates to a method of producing acarbon-based material, the method comprising:

(a) mixing an elastomer and at least a first carbon material anddispersing the first carbon material by applying a shear force to obtaina composite elastomer;

(b) heat-treating the composite elastomer to vaporize the elastomerincluded in the composite elastomer to obtain a second carbon material;and

(c) heat-treating the second carbon material together with a substanceincluding an element Y and having a melting point lower than a meltingpoint of the first carbon material to vaporize the substance includingthe element Y.

A second aspect of the invention relates to a carbon-based materialobtained by the above method.

A third aspect of the invention relates to a carbon-based material whichis mixed into a matrix material including aluminum or magnesium,

wherein a surface of a carbon material has a first bonding structure anda second bonding structure,

wherein the first bonding structure is a structure in which an element Xbonds to a carbon atom of the carbon material,

wherein the second bonding structure is a structure in which an elementY bonds to the element X,

wherein the element X includes at least one element selected from boron,nitrogen, oxygen, and phosphorus, and

wherein the element Y includes at least one element selected frommagnesium, aluminum, silicon, calcium, titanium, vanadium, chromium,manganese, iron, nickel, copper, zinc, and zirconium.

A fourth aspect of the invention relates to a carbon-based material,

wherein a surface of a carbon material has a first bonding structure anda second bonding structure, and

wherein the first bonding structure is a structure in which oxygen bondsto a carbon atom of the carbon material, and

wherein the second bonding structure is a structure in which magnesiumbonds to the oxygen.

A fifth aspect of the invention relates to a method of producing acomposite material, the method comprising:

(d) mixing the carbon-based material obtained by the above method with amatrix material.

A sixth aspect of the invention relates to a composite material obtainedby the above method of producing a composite material.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 schematically shows a mixing method for an elastomer and a carbonmaterial utilizing an open-roll method used in one embodiment of theinvention.

FIG. 2 is a schematic configuration diagram of a device for producing acomposite material by using a pressureless permeation method.

FIG. 3 is a schematic configuration diagram of a device for producing acomposite material by using a pressureless permeation method.

FIG. 4 is a schematic diagram showing XPS data on a carbon-basedmaterial obtained in an example according to the invention.

FIG. 5 shows EDS data (carbon) on a composite material obtained in anexample according to the invention.

FIG. 6 shows EDS data (oxygen) on a composite material obtained in anexample according to the invention.

FIG. 7 shows EDS data (magnesium) on a composite material obtained in anexample according to the invention.

DETAILED DESCRIPTION OF THE EMBODIMENT

The invention may provide a carbon-based material exhibiting improvedsurface wettability, and a method of producing the same. The inventionmay also provide a composite material in which a carbon material isuniformly dispersed, and a method of producing the same.

An embodiment of the invention provides a method of producing acarbon-based material, the method comprising:

(a) mixing an elastomer and at least a first carbon material anddispersing the first carbon material by applying a shear force to obtaina composite elastomer;

(b) heat-treating the composite elastomer to vaporize the elastomerincluded in the composite elastomer to obtain a second carbon material;and

(c) heat-treating the second carbon material together with a substanceincluding an element Y and having a melting point lower than a meltingpoint of the first carbon material to vaporize the substance includingthe element Y.

According to the step (a) of the method according to one embodiment ofthe invention, free radicals formed in the elastomer shorn by the shearforce attack the surface of the first carbon material, whereby thesurface of the first carbon material is activated. Therefore, thedispersibility of the first carbon material in the elastomer isimproved. When using carbon nanofibers as the first carbon material, anunsaturated bond or group of the elastomer bonds to an active site ofthe carbon nanofiber, particularly to a terminal radical of the carbonnanofiber, to reduce the aggregating force of the carbon nanofibers,whereby the dispersibility of the carbon nanofibers can be increased.

According to the step (b) of the method according to one embodiment ofthe invention, the second carbon material having an activated surface isobtained by vaporizing the elastomer by the heat treatment. According tothe step (c) of the method according to one embodiment of the invention,the substance including the element Y is vaporized by the heat treatmentso that the element Y adheres to the surface of the second carbonmaterial, whereby a carbon-based material exhibiting improvedwettability with a matrix material is obtained. Therefore, thecarbon-based material obtained by the method according to one embodimentof the invention can be easily utilized for general metalworking such ascasting.

The elastomer according to one embodiment of the invention may be arubber elastomer or a thermoplastic elastomer. When using a rubberelastomer, the elastomer may be in a crosslinked form or anuncrosslinked form. As the raw material elastomer, an uncrosslinked formis used when using a rubber elastomer.

The step (a) of dispersing the carbon material in the elastomer byapplying a shear force may be carried out by using an open-roll methodwith a roll distance of 0.5 mm or less, an internal mixing method, amulti-screw extrusion mixing method, or the like.

An embodiment of the invention provides a carbon-based material,

wherein a surface of a carbon material has a first bonding structure anda second bonding structure, and

wherein the first bonding structure is a structure in which oxygen bondsto a carbon atom of the carbon material, and

wherein the second bonding structure is a structure in which magnesiumbonds to the oxygen.

Am embodiment of the invention provides a method of producing acomposite material, including (d) mixing the carbon-based materialobtained by the method according to the embodiment of the invention witha matrix material.

Since the element Y adheres to the surface of the carbon-based materialobtained according to one embodiment of the invention, the carbon-basedmaterial exhibits excellent wettability with the matrix material of thecomposite material. In particular, when using aluminum or magnesium asthe matrix of the composite material, if an element which makes up analuminum alloy or a magnesium alloy is used as the element Y, since thematrix material and the element Y exhibit excellent wettability, thecarbon-based material and the matrix material also exhibit excellentwettability. Moreover, the carbon-based material can be dispersed in thematrix metal material due to an improvement of the wettability of thecarbon-based material.

Embodiments of the invention are described below in detail withreference to the drawings.

(A) Elastomer

The elastomer may have a molecular weight of 5,000 to 5,000,000, or20,000 to 3,000,000. If the molecular weight of the elastomer is withinthis range, since the elastomer molecules are entangled and linked, theelastomer easily enters the space in the aggregated first carbonmaterial (e.g. carbon nanofibers) to exhibit an improved effect ofseparating the carbon nanofibers. If the molecular weight of theelastomer is less than 5,000, since the elastomer molecules cannot besufficiently entangled, the effect of dispersing the first carbonmaterial is reduced even if a shear force is applied in the subsequentstep. If the molecular weight of the elastomer is greater than5,000,000, the elastomer becomes too hard so that processing becomesdifficult.

A network component of the elastomer in an uncrosslinked form may have aspin-spin relaxation time (T2n/30° C.) measured at 30° C. by a Hahn-echomethod using a pulsed nuclear magnetic resonance (NMR) technique of 100to 3,000 μsec, or 200 to 1,000 μsec. If the elastomer has a spin-spinrelaxation time (T2n/30° C.) within the above range, the elastomer isflexible and has a sufficiently high molecular mobility. Therefore, whenmixing the elastomer and the first carbon material, the elastomer caneasily enter the space in the first carbon material due to highmolecular motion. If the spin-spin relaxation time (T2n/30° C.) isshorter than 100 μsec, the elastomer cannot have a sufficient molecularmobility. If the spin-spin relaxation time (T2n/30° C.) is longer than3,000 μsec, since the elastomer tends to flow as a liquid, it becomesdifficult to disperse the first carbon material.

A network component of the elastomer in a crosslinked form may have aspin-spin relaxation time (T2n) measured at 30° C. by a Hahn-echo methodusing a pulsed nuclear magnetic resonance (NMR) technique of 100 to2,000 μsec. The reasons therefor are the same as those described for theuncrosslinked form. Specifically, when crosslinking an uncrosslinkedform which satisfies the above conditions by using the method of theinvention, the spin-spin relaxation time (T2n) of the resultingcrosslinked form almost falls within the above range.

The spin-spin relaxation time obtained by the Hahn-echo method using thepulsed NMR technique is a measure which indicates the molecular mobilityof a substance. In more detail, when measuring the spin-spin relaxationtime of the elastomer by the Hahn-echo method using the pulsed NMRtechnique, a first component having a shorter first spin-spin relaxationtime (T2n) and a second component having a longer second spin-spinrelaxation time (T2nn) are detected. The first component corresponds tothe network component (backbone molecule) of the polymer, and the secondcomponent corresponds to the non-network component (branched componentsuch as terminal chain) of the polymer. The shorter the first spin-spinrelaxation time, the lower the molecular mobility and the harder theelastomer. The longer the first spin-spin relaxation time, the higherthe molecular mobility and the softer the elastomer.

As the measurement method in the pulsed NMR technique, a solid-echomethod, a Carr-Purcell-Meiboom-Gill (CPMG) method, or a 90-degree pulsemethod may be applied instead of the Hahn-echo method. However, sincethe elastomer according to the invention has a medium spin-spinrelaxation time (T2), the Hahn-echo method is most suitable. In general,the solid-echo method and the 90-degree pulse method are suitable formeasuring a short spin-spin relaxation time (T2), the Hahn-echo methodis suitable for measuring a medium spin-spin relaxation time (T2), andthe CPMG method is suitable for measuring a long spin-spin relaxationtime (T2).

At least one of the main chain, side chain, and terminal chain of theelastomer includes an unsaturated bond or a group having affinity to thefirst carbon material, particularly to a terminal radical of the carbonnanofiber, or the elastomer has properties of readily producing such aradical or group. The unsaturated bond or group may be at least oneunsaturated bond or group selected from a double bond, a triple bond,and functional groups such as α-hydrogen, a carbonyl group, a carboxylgroup, a hydroxyl group, an amino group, a nitrile group, a ketonegroup, an amide group, an epoxy group, an ester group, a vinyl group, ahalogen group, a urethane group, a biuret group, an allophanate group,and a urea group.

The carbon nanofiber generally has a structure in which the side surfaceis formed of a six-membered ring of carbon atoms and the end is closedby introduction of a five-membered ring. However, since the carbonnanofiber has a forced structure, a defect tends to occur, so that aradical or a functional group tends to be formed at the defect. In oneembodiment of the invention, since at least one of the main chain, sidechain, and terminal chain of the elastomer includes an unsaturated bondor a group having high affinity (reactivity or polarity) to the radicalof the carbon nanofiber, the elastomer and the carbon nanofiber can bebonded. This enables the carbon nanofibers to be easily dispersed byovercoming the aggregating force of the carbon nanofibers. When mixingthe elastomer and the first carbon material such as the carbonnanofibers, free radicals produced by breakage of the elastomer moleculeattack the defects of the carbon nanofibers to produce free radicals onthe surfaces of the carbon nanofibers.

As the elastomer, an elastomer such as natural rubber (NR), epoxidizednatural rubber (ENR), styrene-butadiene rubber (SBR), nitrile rubber(NBR), chloroprene rubber (CR), ethylene propylene rubber (EPR or EPDM),butyl rubber (IIR), chlorobutyl rubber (CIIR), acrylic rubber (ACM),silicone rubber (Q), fluorine rubber (FKM), butadiene rubber (BR),epoxidized butadiene rubber (EBR), epichlorohydrin rubber (CO or CEO),urethane rubber (U), or polysulfide rubber (T); a thermoplasticelastomer such as an olefin-based elastomer (TPO), poly(vinylchloride)-based elastomer (TPVC), polyester-based elastomer (TPEE),polyurethane-based elastomer (TPU), polyamide-based elastomer (TPEA), orstyrene-based elastomer (SBS); or a mixture of these elastomers may beused. In particular, a highly polar elastomer which readily producesfree radicals during mixing of the elastomer, such as natural rubber(NR) or nitrile rubber (NBR), is preferable. An elastomer having a lowpolarity, such as ethylene propylene rubber (EPDM), may also be used inthe invention, since such an elastomer also produces free radicals bysetting the mixing temperature at a relatively high temperature (e.g. 50to 150° C. for EPDM).

The composite elastomer according to one embodiment of the invention maybe directly used as an elastomer material in the form of a crosslinkedelastomer, an uncrosslinked elastomer, or a thermoplastic polymer.

(B) First Carbon Material

As the first carbon material, a carbon allotrope may be used. Forexample, the first carbon material may be selected from carbon fiber,carbon black, amorphous carbon, graphite, diamond, fullerene, and thelike. The carbon fiber used herein includes carbon nanofiber. When usingcarbon black, since the carbon black is inexpensive and many grades arecommercially available, the carbon black can be relatively easilyutilized. A nanomaterial such as a minute carbon material (e.g. carbonnanofiber or fullerene) achieves a high reinforcement effect with asmall amount of addition.

The amount of the first carbon material to be added may be determineddepending on the type and the application of the carbon-based material.

As the carbon black used in the invention, carbon black of variousgrades produced by using various raw materials may be used. The carbonblack may be in a state of either elementary particles (primaryparticles) or an aggregate in which the elementary particles are fusedand connected (agglomerate). However, carbon black having acomparatively high structure in which the aggregate is grown ispreferable when used as a reinforcement filler.

The carbon black used in the invention has an average elementaryparticle diameter of preferably 100 nm or less, and still morepreferably 50 nm or less. The volume effect and the reinforcing effectare increased as the size of the carbon black particle becomes smaller.In practical application, the average particle diameter is preferably 10to 30 nm.

The size of the carbon black particle is also indicated by the nitrogenadsorption specific surface area. In this case, the nitrogen adsorptionspecific surface area is 10 m²/g or more, and preferably 40 m²/g or moreas the nitrogen adsorption specific surface area (m²/g) measuredaccording to JIS K 6217-2 (2001) “Carbon black for rubberindustry—Fundamental characteristics—Part 2: Determination of specificsurface area—Nitrogen adsorption methods—Single-point procedures”.

The reinforcing effect of the carbon black used in the invention isaffected by the degree of structure of the aggregate in which theelementary particles are fused. The reinforcing effect is increased byadjusting the DBP absorption to 50 cm³/100 g or more, and preferably 100cm³/100 g or more. This is because the aggregate forms a higherstructure as the DBP absorption is greater.

As the carbon black used in the invention, carbon black of grades suchas SAF-HS (N134, N121), SAF (N110, N115), ISAF-HS (N234), ISAF (N220,N220M), ISAF-LS (N219, N231), ISAF-HS (N285, N229), HAF-HS (N339, N347),HAF (N330), HAF-LS (N326), T-HS (N351, N299), T-NS (N330T), MAF (N550M),FEF (N550), GPF (N660, N630, N650, N683), SRF-HS-HM (N762, N774), SRF-LM(N760M, N754, N772, N762), FT, HCC, HCF, MCC, MCF, LEF, MFF, RCF, andRCC, and conductive carbon black such as Tokablack, HS-500, acetyleneblack, and Ketjenblack may be used.

When the first carbon material is carbon fiber, particularly carbonnanofiber, the composite elastomer according to one embodiment of theinvention preferably includes the carbon nanofibers in an amount of 0.01to 50 wt %.

The carbon nanofibers preferably have an average diameter of 0.5 to 500nm. In order to increase the strength of the composite elastomer, theaverage diameter of the carbon nanofibers is still more preferably 0.5to 30 nm. The carbon nanofiber may be either a linear fiber or a curvedfiber.

As examples of the carbon nanofiber, a carbon nanotube and the like canbe given. The carbon nanotube has a single-layer structure in which agraphene sheet of a hexagonal carbon layer is closed in the shape of acylinder, or a multi-layer structure in which the cylindrical structuresare nested. Specifically, the carbon nanotube may be formed only of thesingle-layer structure or the multi-layer structure, or may have thesingle-layer structure and the multi-layer structure in combination. Acarbon material having a partial carbon nanotube structure may also beused. The carbon nanotube may be called a graphite fibril nanotube.

A single-layer carbon nanotube or a multi-layer carbon nanotube isproduced to a desired size by using an arc discharge method, a laserablation method, a vapor-phase growth method, or the like.

In the arc discharge method, an arc is discharged between electrodematerials made of carbon rods in an argon or hydrogen atmosphere at apressure slightly lower than atmospheric pressure to obtain amulti-layer carbon nanotube deposited on the cathode. When a catalystsuch as nickel/cobalt is mixed into the carbon rod and an arc isdischarged, a single-layer carbon nanotube is obtained from sootadhering to the inner side surface of a processing vessel.

In the laser ablation method, a target carbon surface into which acatalyst such as nickel/cobalt is mixed is irradiated with strong pulselaser light from a YAG laser in a noble gas (e.g. argon) to melt andvaporize the carbon surface to obtain a single-layer carbon nanotube.

In the vapor-phase growth method, a carbon nanotube is synthesized bythermally decomposing hydrocarbons such as benzene or toluene in a vaporphase. As specific examples of the vapor-phase growth method, a floatingcatalyst method, a zeolite-supported catalyst method, and the like canbe given.

The carbon material may be provided with improved adhesion to andwettability with the elastomer by subjecting the carbon material to asurface treatment such as an ion-injection treatment, sputter-etchingtreatment, or plasma treatment before mixing the carbon material intothe elastomer.

(C) Element Y

The element Y bonds to the surface of the second carbon material toimprove the wettability between the carbon-based material and the matrixmaterial. A carbon material generally exhibits poor wettability with ametal material such as aluminum and magnesium. However, the wettabilityis improved by using the carbon-based material having the element Y onthe surface. A particulate substance including the element Y may bemixed and dispersed in the elastomer in advance so that the first carbonmaterial is more favorably dispersed when mixing the first carbonmaterial into the elastomer. In this case, in the step (a), thesubstance including the element Y may be mixed into the elastomer beforemixing the first carbon material, or may be mixed into the elastomertogether with the first carbon material.

The substance including the element Y preferably has an average particlediameter greater than the average diameter of the first carbon materialused. The average particle diameter of the substance including theelement Y is 500 μm or less, and preferably 1 to 300 μm. The shape ofthe substance including the element Y is not limited to spherical. Thesubstance including the element Y may be in the shape of a sheet orscale insofar as turbulent flows occur around the substance includingthe element Y during mixing.

The substance including the element Y is preferably a metal or semimetalhaving a melting point lower than the melting point of the first carbonmaterial, and still more preferably a low-melting-point(high-vapor-pressure) metal or semimetal having a melting point of 1000°C. or less. If the melting point of the substance including the elementY satisfies the above condition, the substance including the element Ycan be vaporized by the heat treatment in the step (b) without damagingthe carbon material.

When the carbon-based material is mixed into an aluminum or magnesiummatrix material, the element Y preferably includes at least one elementselected from magnesium, aluminum, silicon, calcium, titanium, vanadium,chromium, manganese, iron, nickel, copper, zinc, and zirconium.Therefore, the substance including the element Y may include at leastone element Y selected from these elements. These elements are used aselements which make up an aluminum alloy or a magnesium alloy. Theseelements easily bond to aluminum or magnesium, and can stably exist in astate in which the elements bond to aluminum or magnesium. As theelement Y, magnesium, zinc, or aluminum, which exhibits particularlyexcellent bonding properties with magnesium or aluminum as the matrixmaterial, may be used. In particular, when oxygen bonds to the surfaceof the first carbon material as the element X, it is preferable to usemagnesium as the element Y since magnesium easily bonds to oxygen.Therefore, the carbon-based material thus obtained has a first bondingstructure and a second bonding structure on the surface of the carbonmaterial, the first bonding structure being a structure in which theelement X bonds to the carbon atom of the carbon material and the secondbonding structure being a structure in which the element Y bonds to theelement X. In particular, when the first bonding structure is astructure in which oxygen bonds to the carbon atom of the carbonmaterial, it is preferable that the second bonding structure be astructure in which magnesium bonds to oxygen.

The above description illustrates the case of mixing the substanceincluding the element Y with the elastomer in the step (a). However, theinvention is not limited thereto. It suffices that the substanceincluding the element Y be subjected to the heat treatment in the step(c) together with the second carbon material. For example, the substanceincluding the element Y may be disposed in a heat treatment furnacetogether with the second carbon material and vaporized by the heattreatment in the step (c). In this case, the substance including theelement Y may not be particulate.

In the invention, magnesium or aluminum used as the matrix materialincludes an alloy containing magnesium or aluminum as the majorcomponent.

(D) Step (a) of Mixing Carbon Material into Elastomer and DispersingCarbon Material by Applying Shear Force

The step (a) of dispersing the carbon material in the elastomer byapplying a shear force may be carried out by using an open-roll method,an internal mixing method, a multi-screw extrusion mixing method, or thelike.

In one embodiment of the invention, an example using an open-roll methodwith a roll distance of 0.5 mm or less is described below as the step ofmixing the substance including the element Y and the first carbonmaterial into the elastomer.

FIG. 1 is a diagram schematically showing the open-roll method using tworolls. In FIG. 1, a reference numeral 10 indicates a first roll, and areference numeral 20 indicates a second roll. The first roll 10 and thesecond roll 20 are disposed at a predetermined distance d of preferably1.0 mm or less, and still more preferably 0.1 to 0.5 mm. The first andsecond rolls are rotated normally or reversely. In the example shown inFIG. 1, the first roll 10 and the second roll 20 are rotated in thedirections indicated by the arrows. When the surface velocity of thefirst roll 10 is indicated by V1 and the surface velocity of the secondroll 20 is indicated by V2, the surface velocity ratio (V1/V2) of thefirst roll 10 to the second roll 20 is preferably 1.05 to 3.00, andstill more preferably 1.05 to 1.2. A desired shear force can be obtainedby using such a surface velocity ratio. When causing an elastomer 30 tobe wound around the second roll 20 while rotating the first and secondrolls 10 and 20, a bank 32 of the elastomer is formed between the rolls10 and 20. After the addition of a substance including the element Y tothe bank 32, the elastomer 30 and the substance including the element Yare mixed by rotating the first and second rolls 10 and 20. After theaddition of a first carbon material 40 to the bank 32 in which theelastomer 30 and the substance including the element Y are mixed, thefirst and second rolls 10 and 20 are rotated. After reducing thedistance between the first and second rolls 10 and 20 to the distance d,the first and second rolls 10 and 20 are rotated at a predeterminedsurface velocity ratio. This causes a high shear force to be applied tothe elastomer 30, so that the aggregated first carbon material isseparated by the shear force so that portions of the first carbonmaterial are removed one by one and become dispersed in the elastomer30. The shear force caused by the rolls causes turbulent flows to occuraround the substance including the element Y dispersed in the elastomer.These complicated flows cause the first carbon material to be furtherdispersed in the elastomer 30. If the elastomer 30 and the first carbonmaterial 40 are mixed before mixing the substance including the elementY, since the movement of the elastomer 30 is restrained by the firstcarbon material 40, it becomes difficult to mix the substance includingthe element Y. Therefore, it is preferable to mix the substanceincluding the element Y before adding the carbon material 40 to theelastomer 30.

In the step (a), free radicals are produced in the elastomer shorn bythe shear force and attack the surface of the first carbon material,whereby the surface of the first carbon material is activated. Whenusing natural rubber (NR) as the elastomer, the natural rubber (NR)molecule is cut while being mixed by the rolls to have a molecularweight lower than the molecular weight before being supplied to the openrolls. Since radicals are produced in the cut natural rubber (NR)molecule and attack the surface of the first carbon material duringmixing, the surface of the first carbon material is activated.

In the step (a), the elastomer and the first carbon material are mixedat a relatively low temperature of preferably 0 to 50° C., and stillmore preferably 5 to 30° C. in order to obtain as high a shear force aspossible. In the case of using the open-roll method, it is preferable toset the roll temperature at the above-mentioned temperature. Thedistance d between the first and second rolls 10 and 20 is set to begreater than the average particle diameter of the substance includingthe element Y even when the distance is minimized. This enables thefirst carbon material 40 to be uniformly dispersed in the elastomer 30.

Since the elastomer according to one embodiment of the invention has theabove-described characteristics, specifically, the above-describedmolecular configuration (molecular length), molecular motion, andchemical interaction with the carbon material, dispersion of the firstcarbon material is facilitated. Therefore, a composite elastomerexhibiting excellent dispersibility and dispersion stability (firstcarbon material rarely reaggregates) can be obtained. In more detail,when mixing the elastomer and the first carbon material, the elastomerhaving an appropriately long molecular length and a high molecularmobility enters the space in the first carbon material, and a specificportion of the elastomer bonds to a highly active site of the firstcarbon material through chemical interaction. When a high shear force isapplied to the mixture of the elastomer and the first carbon material inthis state, the first carbon material moves accompanying the movement ofthe elastomer, whereby the aggregated first carbon material is separatedand dispersed in the elastomer. The dispersed first carbon material isprevented from reaggregating due to chemical interaction with theelastomer, whereby excellent dispersion stability can be obtained.

Moreover, since a predetermined amount of the substance including theelement Y is included in the elastomer, a shear force is also applied inthe direction in which the carbon material is separated due to a numberof complicated flows such as turbulent flows of the elastomer occurringaround the substance including the element Y. Therefore, even carbonnanofibers with a diameter of about 30 nm or less or carbon nanofibersin the shape of a curved fiber move in the flow direction of eachelastomer molecule bonded to the carbon nanofibers due to chemicalinteraction, whereby the carbon nanofibers are uniformly dispersed inthe elastomer.

In the step of dispersing the first carbon material in the elastomer byapplying a shear force, the above-mentioned internal mixing method ormulti-screw extrusion mixing method may be used instead of the open-rollmethod. In other words, it suffices that this step apply a shear forceto the elastomer sufficient to separate the aggregated first carbonmaterial.

A composite elastomer obtained by the step of mixing and dispersing thesubstance including the element Y and the first carbon material in theelastomer (mixing and dispersing step) may be crosslinked using acrosslinking agent and formed thereafter, or may be formed withoutcrosslinking the composite elastomer. As the forming method, acompression forming process, an extrusion forming process, or the likemay be used. The compression forming process includes forming thecomposite elastomer, in which the substance including the element Y andthe first carbon material are dispersed, in a pressurized state for apredetermined time (e.g. 20 min) in a forming die having a desired shapeand set at a predetermined temperature (e.g. 175° C.).

In the mixing and dispersing step of the elastomer and the first carbonmaterial, or in the subsequent step, a compounding ingredient usuallyused in the processing of an elastomer such as rubber may be added. Asthe compounding ingredient, a known compounding ingredient may be used.As examples of the compounding ingredient, a crosslinking agent,vulcanizing agent, vulcanization accelerator, vulcanization retarder,softener, plasticizer, curing agent, reinforcing agent, filler, agingpreventive, colorant, and the like can be given.

(E) Composite Elastomer Obtained by Above-Described Method

In the composite elastomer according to one embodiment of the invention,the first carbon material is uniformly dispersed in the elastomer as thematrix. In other words, the elastomer is restrained by the first carbonmaterial. The mobility of the elastomer molecules restrained by thefirst carbon material is small in comparison with the case where theelastomer molecules are not restrained by the first carbon material.Therefore, the first spin-spin relaxation time (T2n), the secondspin-spin relaxation time (T2nn), and the spin-lattice relaxation time(T1) of the carbon fiber composite material according to one embodimentof the invention are shorter than those of the elastomer which does notcontain the first carbon material. In particular, when mixing the firstcarbon material into the elastomer containing the substance includingthe element Y, the second spin-spin relaxation time (T2nn) becomesshorter than that of an elastomer including only the first carbonmaterial. The spin-lattice relaxation time (T1) of the crosslinked formchanges in proportion to the amount of the first carbon material mixed.

In a state in which the elastomer molecules are restrained by the firstcarbon material, the number of non-network components (non-reticulatechain components) may be reduced for the following reasons.Specifically, when the molecular mobility of the entire elastomer isdecreased by the first carbon material, since the number of non-networkcomponents which cannot easily move is increased, the non-networkcomponents tend to behave in the same manner as the network components.Moreover, since the non-network components (terminal chains) easilymove, the non-network components tend to be adsorbed on the active sitesof the first carbon material. It is considered that these phenomenadecrease the number of non-network components. Therefore, the fraction(fnn) of components having the second spin-spin relaxation time becomessmaller than that of the elastomer which does not contain the firstcarbon material. In particular, when mixing the first carbon materialinto the elastomer containing the substance including the element Y, thefraction (fnn) of components having the second spin-spin relaxation timeis further reduced in comparison with the elastomer containing only thefirst carbon material.

Therefore, the composite elastomer according to one embodiment of theinvention preferably has values measured by the Hahn-echo method usingthe pulsed NMR technique within the following range.

Specifically, it is preferable that, in the uncrosslinked form, thefirst spin-spin relaxation time (T2n) measured at 150° C. be 100 to3,000 μsec, the second spin-spin relaxation time (T2nn) measured at 150°C. be absent or 1,000 to 10,000 μsec, and the fraction (fnn) ofcomponents having the second spin-spin relaxation time be less than 0.2.

The spin-lattice relaxation time (T1) measured by the Hahn-echo methodusing the pulsed NMR technique is a measure which indicates themolecular mobility of a substance in the same manner as the spin-spinrelaxation time (T2). In more detail, the shorter the spin-latticerelaxation time of the elastomer, the lower the molecular mobility andthe harder the elastomer. The longer the spin-lattice relaxation time ofthe elastomer, the higher the molecular mobility and the softer theelastomer.

The composite elastomer according to one embodiment of the inventionpreferably has a flow temperature, determined by temperature dependencemeasurement of dynamic viscoelasticity, 20° C. or more higher than theflow temperature of the raw material elastomer. In the compositeelastomer according to one embodiment of the invention, the substanceincluding the element Y and the carbon material are uniformly dispersedin the elastomer. In other words, the elastomer is restrained by thefirst carbon material as described above. In this state, the elastomerexhibits molecular motion smaller than that of the elastomer which doesnot contain the first carbon material, whereby the flowability isdecreased. The composite elastomer according to one embodiment of theinvention having such flow temperature characteristics shows a smalltemperature dependence of dynamic viscoelasticity to exhibit excellentthermal resistance.

(F) Step (b) of Heat-Treating Composite Elastomer to Produce SecondCarbon Material

The second carbon material, in which the first carbon material isdispersed around the substance including the element Y, can be producedby the step (b) of heat-treating the composite elastomer to vaporize theelastomer included in the composite elastomer. The second carbonmaterial activated by the step (a) is produced by the step (b) ofvaporizing the elastomer. Since the surface of the second carbonmaterial has been activated by free radicals of the elastomer moleculesshorn by the step (a), the surface of the second carbon material caneasily bond to the substance including the element Y in the step (c),for example.

The heat treatment conditions may be arbitrarily selected depending onthe type of the elastomer used. The heat treatment temperature is set ata point equal to or higher than the vaporization temperature of theelastomer and lower than the vaporization temperature of the firstcarbon material.

The step (b) is performed in the presence of a substance including theelement X so that the second carbon material in which the element Xbonds to the carbon atom of the first carbon material can be obtained.For example, the composite elastomer may include the substance includingthe element X, and the element X may be caused to bond to the carbonatom of the first carbon material by the heat treatment in the step (b).Or, the step (b) may be performed in an atmosphere containing thesubstance including the element X so that the element X is caused tobond to the carbon atom of the first carbon material, for example.

The element X is an element which easily bonds to the carbon materialvia a covalent bond and is a light element with a valence of preferablytwo or more. The element X may include at least one element selectedfrom boron, nitrogen, oxygen, and phosphorus. The element X ispreferably oxygen or nitrogen. In particular, since oxygen is present inair, oxygen can be easily used in the heat treatment in the step (b).Moreover, oxygen easily reacts with the activated first carbon materialsuch as a radical of carbon nanofiber. Therefore, it is preferable touse oxygen as the element X. Moreover, since oxygen easily bonds to ametal material such as magnesium, the second carbon material to whichoxygen bonds can easily bond to the metal or semimetal element Y.

When using oxygen as the element X, the atmosphere used for the heattreatment in the step (b) may contain oxygen. When using nitrogen as theelement X, the step (b) may be carried out in an ammonium gasatmosphere. When using boron or phosphorus as the element X, thesubstance including the element X may be mixed into the elastomer beforethe step (b). In this case, the substance including the element X may bemixed during mixing in the step (a), for example.

In the step (b) according to one embodiment of the invention, thecomposite elastomer obtained by the step (a) is disposed in a heattreatment furnace, and the atmosphere inside the furnace is heated tothe vaporization temperature of the elastomer (e.g. 500° C.). Theelastomer is vaporized by heating and the surface of the first carbonmaterial activated by the step (a) bonds to the element X included inthe atmosphere inside the furnace or in the elastomer, whereby thesurface-treated second carbon material can be produced. Since thesurface of the second carbon material has been activated by freeradicals of the elastomer molecules shorn by the step (a), the surfaceof the second carbon material can easily bond to oxygen present in theatmosphere inside the furnace, for example. Since the surface of thesecond carbon material thus obtained has been oxidized and activated,the second carbon material easily bonds to the metal or semimetalelement Y. In addition, since the surface of the second carbon materialhas been activated by the reaction with the radicals of the elastomer,the surface of the second carbon material easily bonds to the element Yeven if the element X is not used.

(G) Step (c) of Heat-Treating Second Carbon Material Together withSubstance Including Element Y to Vaporize Substance Including Element Y

The carbon-based material according to the invention can be produced bythe step (c) of heat-treating the second carbon material obtained by thestep (b) together with the substance including the element Y having amelting point lower than the melting point of the first carbon materialto vaporize the substance including the element Y.

The heat treatment temperature in the step (c) is set at a point higherthan the heat treatment temperature in the step (b), equal to or higherthan the vaporization temperature of the substance including the elementY, and lower than the vaporization temperature of the first carbonmaterial. The heat treatment in the step (c) may be performed at thesame time as the step (b) by setting the heat treatment temperature inthe step (b) at a point equal to or higher than the vaporizationtemperature of the substance including the element Y, or the step (b)may be performed in the process of increasing the temperature from roomtemperature to the heat treatment temperature in the step (c).

When the second carbon material obtained by the step (b) and thesubstance including the element Y are heated to a temperature equal toor higher than the vaporization temperature of the substance includingthe element Y in a heat treatment furnace, the substance including theelement Y is vaporized so that the element Y bonds to the surface of thesecond carbon material or the element Y bonds to the element X bonded tothe surface of the second carbon material to obtain the carbon-basedmaterial according to the invention.

The substance including the element Y may be mixed into the compositeelastomer in advance by mixing the substance including the element Y andthe elastomer in the step (a) as stated above, or may not be mixed intothe composite elastomer. When the substance including the element Y isnot mixed into the composite elastomer in advance, the substanceincluding the element Y may be disposed in a heat treatment furnace inthe step (c) in addition to the second carbon material. The element Yvaporized by the heat treatment bonds to the element X bonded to thesurface of the second carbon material. In the step (c), a desiredcarbon-based material can be obtained by disposing the second carbonmaterial in the presence of the substance including the element Y whichhas been vaporized.

The vaporized element Y easily bonds to the element X on the surface ofthe second carbon material so that a compound of the element X and theelement Y is produced. The element X prevents direct bonding between theelement Y and the first carbon material. For example, when the element Yis aluminum, if the first carbon material directly bonds to aluminum, asubstance which easily reacts with water, such as Al₄C₃, is produced.Therefore, it is preferable to perform the step (b) of causing theelement X to bond to the surface of the first carbon material before thestep (c) of vaporizing the material Y.

The surface of the carbon-based material (e.g. carbon nanofiber) thusobtained has a structure in which the carbon atom of the carbonnanofiber bonds to the element X and the element X bonds to the elementY. Therefore, the surface of the carbon-based material (e.g. carbonnanofiber) has a structure in which the surface is covered with thecompound layer (e.g. oxide layer) of carbon and the element X and isalso covered with the reaction product layer of the element X and theelement Y (e.g. magnesium). The surface structure of the carbon-basedmaterial may be analyzed by X-ray photoelectron spectroscopy (XPS) orenergy dispersive spectrum (EDS) analysis.

(H) Step (d) of Obtaining Composite Material by Using Carbon-BasedMaterial

In the step (d) according to one embodiment of the invention, thecarbon-based material obtained according to the above-describedembodiment is mixed with a matrix material to produce a compositematerial in which the carbon material is dispersed in the matrixmaterial.

As the matrix material, a metal used in a general casting process may beselected. In particular, light metals such as aluminum and an aluminumalloy and magnesium and a magnesium alloy are preferable.

In the step (d), various forming methods such as methods described belowmay be employed.

(d-1) Powder Forming Method

A powder forming step of the composite material according to oneembodiment of the invention may be performed by powder forming thecarbon-based material obtained by the above-described step (c). In moredetail, the carbon-based material obtained according to theabove-described embodiment is compressed in a die after mixing with thematrix material, and sintered at the sintering temperature of the matrixmaterial (e.g. 550° C. when the matrix material is aluminum) to obtain acomposite material, for example.

The powder forming according to one embodiment of the invention is thesame as powder forming in a metal forming process and involves powdermetallurgy. The powder forming according to one embodiment of theinvention not only includes the case of using a powder raw material, butalso includes the case of using a raw material formed in the shape of ablock by compression-preforming the carbon-based material. As the powderforming method, a general sintering method, a spark plasma sintering(SPS) method using a plasma sintering device, or the like may beemployed.

The carbon-based material and particles of the matrix material may bemixed by dry blending, wet blending, or the like. When using wetblending, it is preferable to mix (wet-blend) the matrix material withthe powder of the carbon-based material in a solvent. Even when thecarbon-based material maintains the external shape of the compositeelastomer due to bonding between the elements Y, since the bonding forcebetween the elements Y is small, the carbon-based material can be easilyground. Therefore, since the carbon-based material which is ground topowder such as particles or fibers can be used when dry blending or wetblending the carbon-based material, the carbon-based material is easilyutilized for metalworking.

The composite material produced by such powder forming is obtained in astate in which the carbon-based material is dispersed in the matrixmaterial. The particles of the matrix material used in the step (d) maybe formed of a material containing the element Y or a material whichdoes not contain the element Y. A composite material having desiredproperties can be produced by adjusting the mixing ratio of thecarbon-based material to the matrix material.

(d-2) Casting Method

A casting step of the composite material may be performed by mixing thecarbon-based material obtained according to the above-describedembodiment into the matrix material such as a molten metal, and castingthe mixture in a die having a desired shape, for example. In the castingstep, a metal mold casting method, a diecasting method, or alow-pressure casting method, in which a molten metal is poured into adie made of steel, may be employed. A method classified into a specialcasting method, such as a high-pressure casting method in which a moltenmetal is caused to solidify at a high pressure, a thixocasting method inwhich a molten metal is stirred, or a centrifugal casting method inwhich a molten metal is cast into a die by utilizing centrifugal force,may also be employed. In these casting methods, a molten matrix materialis caused to solidify in a die in a state in which the carbon-basedmaterial is mixed into the molten matrix material to form a compositematerial.

The molten matrix material used in the casting step may be selected frommetals used in a general casting process. In particular, the moltenmatrix material may be appropriately selected from light metals such asaluminum and an aluminum alloy and magnesium and a magnesium alloy,either individually or in combination of two or more, depending on theapplication. If the metal used as the molten metal is a metal the sameas the substance including the element Y bonded to the carbon-basedmaterial, or an alloy containing the identical element Y, thewettability with the element Y is increased, whereby the strength of thecomposite material as the product can be increased. When a materialwhich does not contain the element Y is used as the molten matrixmaterial, a composite material having desired properties can be producedby adjusting the mixing ratio of the carbon-based material to the moltenmatrix material.

(d-3) Permeation Method

In one embodiment of the invention, a casting step using a pressurelesspermeation method which causes a molten metal to permeate thecarbon-based material is described below in detail with reference toFIGS. 2 and 3.

FIGS. 2 and 3 are schematic configuration diagrams of a device forproducing a composite material by using the pressureless permeationmethod. As the carbon-based material obtained according to theabove-described embodiment, a carbon-based material 4 which iscompression-preformed in a forming die having a desired shape may beused. In FIG. 2, the carbon-based material 4 (e.g. carbon-based materialusing carbon nanofibers as first carbon material 40) formed in advanceis placed in a sealed container 1. A matrix material ingot such as analuminum ingot 5 is disposed on the carbon-based material 4. Thecarbon-based material 4 and the aluminum ingot 5 disposed in thecontainer 1 are heated to a temperature equal to or higher than themelting point of aluminum by using heating means (not shown) provided inthe container 1. The heated aluminum ingot 5 is melted to form moltenaluminum (molten metal). The molten aluminum permeates the space in thecarbon-based material 4.

The carbon-based material 4 according to one embodiment of the inventionis formed to have a space which allows the molten aluminum to rapidlypermeate the entire carbon-based material 4 by a capillary phenomenonwhen compression-preforming the carbon-based material 4. If thecarbon-based material 4 maintains a certain shape, the carbon-basedmaterial 4 may not be compression-preformed. The molten aluminumpermeates the carbon-based material 4 so that the carbon-based material4 is completely filled with the molten aluminum. Then, heating using theheating means of the container 1 is terminated so that the molten metalwhich has permeated the carbon-based material 4 is cooled and solidifiedto obtain a composite material 6, as shown in FIG. 3, in which thecarbon-based material 4 is uniformly dispersed. The carbon-basedmaterial 4 is preferably produced by selecting the element Y whicheasily bonds to the molten metal.

The atmosphere inside the container 1 may be removed by decompressionmeans 2 such as a vacuum pump connected with the container 1 beforeheating the container 1. Nitrogen gas may be introduced into thecontainer 1 from inert-gas supply means 3 such as a nitrogen gascylinder connected with the container 1.

In one embodiment of the invention, the carbon-based materialcompression-preformed into a desired shape in advance is used. However,the permeation method may be performed by placing the carbon-basedmaterial which is ground to particles in a die having a desired shape,and placing the matrix material ingot on the carbon-based material.

The above-described embodiment illustrates the pressureless permeationmethod. However, a pressure permeation method which applies pressure byutilizing the pressure of an atmosphere such as an inert gas may also beused, for example.

As described above, since the element Y bonds to the surface of thecarbon-based material in the composite material, the carbon-basedmaterial has improved wettability. Since the carbon-based material hassufficient wettability with the molten matrix material, a homogenouscomposite material of which the difference of the mechanical propertiesis decreased over the entire material is obtained.

Examples according to the invention and comparative examples aredescribed below. However, the invention is not limited to the followingexamples.

EXAMPLES 1 TO 3 And COMPARATIVE EXAMPLE 1 (1) Preparation of Sample (a)Preparation of Uncrosslinked Sample (Composite Elastomer)

Step 1: Open rolls with a roll diameter of six inches (roll temperature:10 to 20° C.) were provided with a predetermined amount (100 g) of apolymer substance (100 parts by weight (phr)) shown in Table 1, and thepolymer substance was wound around the roll.

Step 2: A substance including the element Y was added to the polymersubstance in an amount (parts by weight) shown in Table 1. The rolldistance was set at 1.5 mm. The type of the substance including theelement Y added is described later.

Step 3: A first carbon material (“CNT” in Table 1) was added to thepolymer substance containing the substance including the element Y in anamount (parts by weight) shown in Table 1. The roll distance was set at1.5 mm.

Step 4: After the addition of the first carbon material, the mixture ofthe polymer substance and the first carbon material was removed from therolls.

Step 5: After reducing the roll distance from 1.5 mm to 0.3 mm, themixture was supplied and tight milled. The surface velocity ratio of thetwo rolls was set at 1.1. The tight milling was repeatedly performed tentimes.

Step 6: After setting the rolls at a predetermined distance (1.1 mm),the mixture subjected to tight milling was supplied and sheeted.

Uncrosslinked samples of composite elastomers of Examples 1 to 3 werethus obtained.

As the substance including the element Y in Examples 1 to 3, magnesiumparticles (average particle diameter: 50 μm) were used. As the firstcarbon material in Examples 1 to 3 and the carbon material inComparative Example 1, carbon nanofibers (CNT) having a diameter (fiberdiameter) of about 10 to 20 nm were used.

(b) Preparation of Second Carbon Material

The uncrosslinked sample (composite elastomer) obtained by (a) in eachof Examples 1 to 3 was heat-treated for two hours in a heat treatmentfurnace containing a nitrogen atmosphere at a temperature equal to orhigher than the vaporization temperature of the elastomer (500° C.) tovaporize the elastomer to obtain a second carbon material.

(c) Preparation of Carbon-Based Material

The second carbon material obtained by (b) in each of Examples 1 to 3was heat-treated for one hour in the heat treatment furnace at atemperature equal to or higher than the vaporization temperature (570°C.) of the substance including the element Y (magnesium) to vaporize thesubstance including the element Y (magnesium) to obtain a carbon-basedmaterial.

(d) Preparation of Composite Material

10 g of powder of the carbon-based material obtained by (c) in each ofExamples 1 to 3 and 500 g of aluminum powder were mixed by using a ballmill. The resulting mixed powder was compression-formed in the shape ofa block having dimensions of 30×40×20 mm. After placing an aluminumingot (purity: 99.85%) on the formed product, the formed product and thealuminum ingot were disposed in a heat treatment furnace containing anitrogen atmosphere. The atmosphere inside the heat treatment furnacewas heated to 750° C. to cause the aluminum ingot to melt and permeatethe compression-formed product to obtain a composite material. Thecarbon nanofiber content of the composite material was 1.6 vol %. As thealuminum powder, aluminum particles having a purity of 99.85% and anaverage particle diameter of 28 μm were used.

In Comparative Example 1, carbon nanofibers and aluminum powder weremixed by using a ball mill, and aluminum was caused to permeate theformed product in the same manner as described above to obtain acomposite material of Comparative Example 1.

(2) Measurement Using Pulsed NMR Technique

The uncrosslinked sample was subjected to measurement by the Hahn-echomethod using the pulsed NMR technique. The measurement was conductedusing “JMN-MU25” manufactured by JEOL, Ltd. The measurement wasconducted under conditions of an observing nucleus of ¹H, a resonancefrequency of 25 MHz, and a 90-degree pulse width of 2 μsec, and a decaycurve was determined while changing Pi in the pulse sequence(90°×−Pi−180°×) of the Hahn-echo method. The sample was measured in astate in which the sample was inserted into a sample tube in anappropriate magnetic field range. The measurement temperature was 150°C. The first spin-spin relaxation time (T2n), the second spin-spinrelaxation time (T2nn), and the fraction (fnn) of components having thesecond spin-spin relaxation time were determined for the raw materialelastomer and the uncrosslinked sample of the composite elastomer. Thefirst spin-spin relaxation time (T2n) at a measurement temperature of30° C. was also measured for the raw material elastomer. The measurementresults are shown in Table 1. The second spin-spin relaxation time(T2nn) was not detected in Examples 1 to 3. Therefore, the fraction(fnn) of components having the second spin-spin relaxation time waszero.

(3) Measurement of Flow Temperature

The flow temperature was determined for the raw material elastomer andthe uncrosslinked sample of the composite elastomer by dynamicviscoelasticity measurement (JIS K 6394). In more detail, the flowtemperature was determined by applying a sine vibration (±0.1% or less)to the sample having a width of 5 mm, a length of 40 mm, and a thicknessof 1 mm, and measuring the stress and phase difference δ generated byapplying the sine vibration. The temperature was changed from −70° C. to150° C. at a temperature rise rate of 2° C./min. The results are shownin Table 1. In Table 1, the case where the flow phenomenon of the samplewas not observed up to 150° C. is indicated as “150° C. or higher”.

(4) XPS Analysis of Carbon-Based Material

Table 1 shows XPS analysis results of the carbon-based materialsobtained by (c) in Examples 1 to 3 and the carbon nanofibers ofComparative Example 1. In Table 1, the case where the presence of acarbon-oxygen bond was confirmed on the surface of the carbon-basedmaterial is indicated as “surface oxidation”, and the case where thepresence of a carbon-oxygen bond was not confirmed is indicated as“none”. FIG. 4 shows a schematic diagram of XPS data on the carbon-basedmaterial of Example 1. A first line segment 50 indicates a double bond“C═O”, a second line segment 60 indicates a single bond “C—O”, and athird line segment 70 indicates a carbon-carbon bond.

(5) EDS Analysis of Carbon-Based Material

Table 1 shows EDS analysis results of the composite materials obtainedby (d) in Examples 1 to 3 and the carbon nanofibers of ComparativeExample 1. In Table 1, the case where the presence of magnesium wasconfirmed around the carbon-based material is indicated as “Mg”, and thecase where the presence of magnesium was not confirmed is indicated as“none”. FIGS. 5, 6, and 7 show EPS data on the carbon-based material ofExample 1. FIGS. 5 to 7 show image data obtained by the EDS analysis.Since the presence or absence of elements is unclear in theblack-and-white image, negative-positive inversion processing wasperformed. The black area in FIG. 5 indicates the presence of carbon,that is, the carbon nanofiber as the first carbon material. The blackarea in FIG. 6 indicates the presence of oxygen. The black (dark) areain FIG. 7 indicates the presence of magnesium.

(6) Measurement of Compressive Yield Strength of Composite Material

10×10 mm samples with a thickness of 5 mm were prepared from thecomposite materials obtained by (d) in Examples 1 to 3 and the compositematerial of Comparative Example 1. The 0.2% yield strength (σ0.2) of thesamples when compressing the samples at 0.01 mm/min was measured. Themaximum value, minimum value, and mean value (MPa) of the compressiveyield strength were determined. The results are shown in Table 1.

TABLE 1 Comparative Example 1 Example 2 Example 3 Example 1 Raw materialelastomer Polymer substance Natural rubber (NR) EPDM Nitrile rubber(NBR) — Polar group Double bond Double bond Nitrile group — NorborneneAverage molecular weight 3,000,000 200,000 3,000,000 — T2n (30° C.)(μsec) 700 520 300 — T2n (150° C.) (μsec) 5500 2200 1780 — T2nn (150°C.) (μsec) 18000 16000 13700 — fnn (150° C.) 0.381 0.405 0.133 — Flowtemperature (° C.) 40 55 80 — Amount Polymer (phr) 100 100 100 0Magnesium (phr) 2 2 2 0 CNT (phr) 10 10 10 100 Composite elastomer Flowtemperature (° C.) 150° C. or higher 150° C. or higher 150° C. or higher— (uncrosslinked sample) T2n (150° C.) (μsec) 1850 1760 1230 — T2nn(150° C.) (μsec) None None None — fnn (150° C.) 0 0 0 — ÄT1 (msec/CNT 1vol %) 15.9 16.5 14.2 — XPS analysis result Oxygen on surface ofcarbon-based Surface oxidation Surface oxidation Surface oxidation Nonematerial EDS analysis result Magnesium on surface of carbon- Mg Mg Mg Mgbased material Compressive yield strength Maximum value (MPa) 460 450455 75 of composite material Mean value (MPa) 445 430 435 50 Minimumvalue (MPa) 430 410 420 25

From the results shown in Table 1, the following items were confirmed byExamples 1 to 3 according to the invention. Specifically, the spin-spinrelaxation times at 150° C. (T2n/150° C. and T2nn/150° C.) of theuncrosslinked sample (composite elastomer) containing the substanceincluding the element Y and the first carbon material are shorter thanthose of the raw material elastomer which does not contain the substanceincluding the element Y and the first carbon material. The fraction(fnn/150° C.) of the uncrosslinked sample (composite elastomer)containing the substance including the element Y and the first carbonmaterial is smaller than that of the raw material elastomer which doesnot contain the substance including the element Y and the first carbonmaterial. These results suggest that the first carbon material isuniformly dispersed in the composite elastomer according to the example.

The flow temperature of the composite elastomer (uncrosslinked sample)containing the substance including the element Y and the carbon-basedmaterial is 20° C. or more higher than that of the raw materialelastomer. Therefore, it is understood that the composite elastomer hasa small temperature dependence of dynamic viscoelasticity and exhibitsexcellent thermal resistance.

From the XPS analysis results of the carbon-based materials of Examples1 to 3, it was found that the surface of the second carbon material isoxidized.

From the EDS analysis results of the carbon-based materials of Examples1 to 3, it was found that oxygen and magnesium exist around thecarbon-based material.

It was found that the compressive yield strength of the composite formedproducts of Examples 1 to 3 is significantly higher in the minimum valueand the maximum value than the compressive yield strength of thecomposite material of Comparative Example 1. While the maximum value andthe minimum value of the compressive yield strength of the compositeformed products of Examples 1 to 3 differ from the mean value in therange of ±5%, the maximum value and the minimum value of the compressiveyield strength of the composite material of Comparative Example 1 differfrom the mean value in the range of ±50%. Therefore, it was found thatthe composite materials of Examples 1 to 3 are entirely homogenous.

It was found that the homogenous composite materials, in which thecarbon-based materials of Examples 1 to 3 are uniformly dispersed inaluminum as the matrix material, were obtained. It was also found thatthe wettability between the carbon-based material and aluminum wasimproved as indicated by the significant increase in the compressiveyield strength.

Although only some embodiments of the present invention have beendescribed in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the embodimentswithout materially departing from the novel teachings and advantages ofthis invention. Accordingly, all such modifications are intended to beincluded within scope of this invention.

1. A method of producing a carbon-based material, the method comprising:(a) mixing an elastomer and at least a first carbon material anddispersing the first carbon material by applying a shear force to obtaina composite elastomer; (b) heat-treating the composite elastomer tovaporize the elastomer included in the composite elastomer to obtain asecond carbon material; and (c) heat-treating the second carbon materialtogether with a substance including an element Y and having a meltingpoint lower than a melting point of the first carbon material tovaporize the substance including the element Y.
 2. The method ofproducing a carbon-based material as defined in claim 1, wherein thestep (b) is performed in the presence of a substance including anelement X so that the element X bonds to a carbon atom of the firstcarbon material, and wherein the element X includes at least one elementselected from boron, nitrogen, oxygen, and phosphorus.
 3. The method ofproducing a carbon-based material as defined in claim 2, wherein thecomposite elastomer includes the substance including the element X, andwherein the element X bonds to the carbon atom of the first carbonmaterial by the heat treatment in the step (b).
 4. The method ofproducing a carbon-based material as defined in claim 2, wherein thestep (b) is performed in an atmosphere containing the substanceincluding the element X so that the element X bonds to the carbon atomof the first carbon material.
 5. The method of producing a carbon-basedmaterial as defined in claim 2, wherein the element X is oxygen ornitrogen.
 6. The method of producing a carbon-based material as definedin claim 1, wherein the composite elastomer includes the substanceincluding the element Y.
 7. The method of producing a carbon-basedmaterial as defined in claim 1, wherein, in the step (c), the substanceincluding the element Y is disposed in a heat treatment furnace togetherwith the second carbon material and vaporized by the heat treatment. 8.The method of producing a carbon-based material as defined in claim 1,wherein the carbon-based material is mixed into a matrix materialincluding aluminum, and wherein the substance including the element Yincludes at least one element selected from magnesium, aluminum,silicon, calcium, titanium, vanadium, chromium, manganese, iron, nickel,copper, zinc, and zirconium.
 9. The method of producing a carbon-basedmaterial as defined in claim 1, wherein the carbon-based material ismixed into a matrix material including magnesium, and wherein thesubstance including the element Y includes at least one element selectedfrom magnesium, aluminum, silicon, calcium, titanium, vanadium,chromium, manganese, iron, nickel, copper, zinc, and zirconium.
 10. Themethod of producing a carbon-based material as defined in claim 8,wherein the substance including the element Y includes the element Yselected from magnesium, zinc, and aluminum.
 11. The method of producinga carbon-based material as defined in claim 9, wherein the substanceincluding the element Y includes the element Y selected from magnesium,zinc, and aluminum.
 12. The method of producing a carbon-based materialas defined in claim 1, wherein the first carbon material is carbonblack.
 13. The method of producing a carbon-based material as defined inclaim 1, wherein the first carbon material is carbon fiber.
 14. Themethod of producing a carbon-based material as defined in claim 13,wherein the carbon fiber is carbon nanofiber.
 15. The method ofproducing a carbon-based material as defined in claim 14, wherein thecarbon nanofibers have an average diameter of 0.5 to 500 nm.
 16. Themethod of producing a carbon-based material as defined in claim 1,wherein the elastomer has a molecular weight of 5,000 to 5,000,000. 17.The method of producing a carbon-based material as defined in claim 1,wherein at least one of a main chain, a side chain, and a terminal chainof the elastomer includes at least one unsaturated bond or group havingaffinity to carbon nanofiber and selected from a double bond, a triplebond, and functional groups such as α-hydrogen, a carbonyl group, acarboxyl group, a hydroxyl group, an amino group, a nitrile group, aketone group, an amide group, an epoxy group, an ester group, a vinylgroup, a halogen group, a urethane group, a biuret group, an allophanategroup, and a urea group.
 18. The method of producing a carbon-basedmaterial as defined in claim 1, wherein a network component of theelastomer in an uncrosslinked form has a spin-spin relaxation time (T2n)measured at 30° C. by a Hahn-echo method using a pulsed nuclear magneticresonance (NMR) technique of 100 to 3,000 μsec.
 19. The method ofproducing a carbon-based material as defined in claim 1, wherein anetwork component of the elastomer in a crosslinked form has a spin-spinrelaxation time (T2n) measured at 30° C. by a Hahn-echo method using apulsed nuclear magnetic resonance (NMR) technique of 100 to 2,000 μsec.20. The method of producing a carbon-based material as defined in claim1, wherein the elastomer is natural rubber or nitrile butadiene rubber.21. The method of producing a carbon-based material as defined in claim1, wherein the step (a) is performed by using an open-roll method with aroll distance of 0.5 mm or less.
 22. The method of producing acarbon-based material as defined in claim 21, wherein two rolls used inthe open-roll method have a surface velocity ratio of 1.05 to 3.00. 23.The method of producing a carbon-based material as defined in claim 1,wherein the step (a) is performed by using an internal mixing method.24. The method of producing a carbon-based material as defined in claim1, wherein the step (a) is performed by using a multi-screw extrusionmixing method.
 25. The method of producing a carbon-based material asdefined in claim 1, wherein the step (a) is performed at 0 to 50° C. 26.A carbon-based material obtained by the method as defined in claim 1.27. A carbon-based material which is mixed into a matrix materialincluding aluminum or magnesium, wherein a surface of a carbon materialhas a first bonding structure and a second bonding structure, whereinthe first bonding structure is a structure in which an element X bondsto a carbon atom of the carbon material, wherein the second bondingstructure is a structure in which an element Y bonds to the element X,wherein the element X includes at least one element selected from boron,nitrogen, oxygen, and phosphorus, and wherein the element Y includes atleast one element selected from magnesium, aluminum, silicon, calcium,titanium, vanadium, chromium, manganese, iron, nickel, copper, zinc, andzirconium.
 28. A carbon-based material, wherein a surface of a carbonmaterial has a first bonding structure and a second bonding structure,and wherein the first bonding structure is a structure in which oxygenbonds to a carbon atom of the carbon material, and wherein the secondbonding structure is a structure in which magnesium bonds to the oxygen.29. A method of producing a composite material, the method comprising:(d) mixing the carbon-based material obtained by the method as definedin claim 1 with a matrix material.
 30. A composite material obtained bythe method as defined in claim 29.